A hardware problem of a photographing device or processing through some image algorithms (for example, an image smoothing algorithm) tends to blur a border or an outline in an image. Image sharpening is a method for compensating an outline of an image and enhancing an edge and a gray level jump part of the image, so as to make the image clear. In view of a frequency domain, an image is blurred because its high-frequency component is attenuated. Therefore, an idea of the image sharpening is that a high-pass filter is mainly used to extract high-frequency information from an image and the extracted high-frequency information is superimposed on the original image to make the image clear.
Currently, in a commonly used image sharpening method, a high-pass filter, that is, a Laplacian, is used to perform a Laplacian operation on a luminance component of an image to obtain its high-frequency information, for example, edge information and outline information of the image, and corresponding pixels of the original image and an image that has undergone the Laplacian operation are directly added up, so as to achieve an objective of enhancing an edge and an outline of the image and making the image look clearer. However, in this method, after the image that has undergone the Laplacian operation is superimposed on the original image, overshoot and undershoot tend to occur at a bright-dark boundary. Such phenomena are manifested in the image as a “white margin” and a “black margin” that are produced at a black-white edge. That is, a halo (halo) effect occurs, and a sharpening effect of the image is relatively poor.